1. Field of the Invention
The present invention generally relates to implantable medical devices, and more particularly, relates to implantable medical devices which provide non-tetanic stimulation of skeletal muscle tissue.
2. Description of the Prior Art
The medical characteristics of sleep apnea have been known for some time. There are two generally recognized forms of the disease. The first is central sleep apnea which is associated with the failure of the body to automatically generate the neuro-muscular stimulation necessary to initiate and control a respiratory cycle at the proper time. Work associated with employing electrical stimulation to treat this condition is discussed in "Diaphragm Pacing: Present Status", by William W. L. Glenn, in Pace, Volume I, at pages 357-370 (July-September 1978).
The second condition is known as obstructive sleep apnea. It is discussed at some length in "Obstructive Sleep Apnea: Diagnosis and Treatment", by Drs. Cook and Osguthorpe in Journal of South Carolina Medical Association, 81 (12): 647-651 (December, 1985). Additional references treating the subject include: "Physiologic Basis of Therapy for Sleep Apnea", by K. P. Strohl, N. S. Cherniack, and B. Gothe in American Review of Respiratory Disease, Volume 134, pp. 791-802 (1986); and "Obstructive Sleep Apnea Syndrome", by J. Kaplan and B. A. Staats in Mayo Clinic Proceedings, Volume 65, pp. 1087-1094 (1990).
Electrical stimulation of muscle tissue has been used for some time. Much work has been done in this area in cardiac pacing, for example. Paul E. Ciske and John A. Faulkner in "Chronic Electrical Stimulation of Nongrafted and Grafted Skeletal Muscles in Rats", in Journal of Applied Physiology, Volume 59(5), pp. 1434-1439 (1985), discuss some physiological effects of chronic stimulation.
At present, a tracheostomy may be the treatment of choice for a number of patients when obstructive sleep apnea is severe. However, some interest has been displayed in electrical stimulation of the muscle tissue along the upper airway during respiration. U.S. Pat. No. 4,830,008 issued to Meer discusses a technique for electrical stimulation of the muscles of the upper airway in synchrony with the respiratory cycle. U.S. Pat. No. 4,506,666 issued to Durkan discusses such stimulation in conjunction with pressurized airflow supplied by a respirator. A similar approach is discussed by Miki et al., in "Effects of Submental Electrical Stimulation During Sleep on Upper Airway Patency in Patients with Obstructive Sleep Apnea" in American Review of Respiratory Disease, Volume 140, pp. 1285-1289 (1989).
The electrical stimulation of the prior art techniques, however, are primarily concerned with causing contractile motion of the stimulated muscle. This means that the stimulation energy must necessarily be relatively large and the effects of the stimulation are directly cognizable by the patient.